A plot to abduct and film the beheading of a young British Muslim soldier - apparently inspired by footage of Iraqi murders posted on the internet - was foiled yesterday with the arrest of nine men, according to police and security sources.

In what would mark a new departure for UK jihadists, members of the group are alleged to have been preparing to film the kidnap victim as he begged for mercy before being murdered, and were then planning to post the footage on the web.

The conspiracy is alleged to have been intended to echo the deaths of hostages in Iraq such as Ken Bigley and Margaret Hassan, according to security sources, but to the incredulity of the local community.

Whitehall sources confirmed last night that the joint West Midlands police and security service operation was prompted by fears that the alleged plotters were too close to endangering public safety to allow the "potential risk" to continue. They refused to be drawn on the plot further, but added: "It is significant insofar as it shows a continued commitment on the part of extremists to carry out operations in this country and the fact that it is different to what we have seen before."

Eight men were arrested in raids before dawn at their homes across Birmingham yesterday, while a ninth was seized later in the day as he drove out of the city along the M6 motorway. Those who were identified by relatives and neighbours were mostly in their late 20s and early 30s, and included at least two shopkeepers and one businessman. There were unconfirmed reports yesterday that all those arrested were Britons of Pakistani origin.

The man alleged to have been the intended victim, a lance corporal in his 20s, was taken into police protective custody yesterday along with several members of his family amid reports that two other men had evaded arrest. He had recently arrived home on leave after a tour of duty in Afghanistan, and police and the security service, MI5, believe he was to have been bundled into a van as he walked along a street and driven to a pre-prepared cell where he could be filmed. There, they allege, he was likely to have been tortured and eventually beheaded.

The operation appears to underline recent warnings by senior police and the security service that the UK could be particularly vulnerable to attack by al-Qaida because of its traditional links with Pakistan. Detectives from the newly-formed Midlands Counter Terrorism Unit carried out the raids at 4am at houses in the Sparkhill, Washwood Heath, Kingstanding and Edgbaston areas of Birmingham.

West Midlands police said the men had been arrested "on suspicion of the commission, preparation or instigation of acts of terrorism under the Terrorism Act 2000". Four other premises - an internet cafe, two Islamic bookshops and a grocery store - were also raided and were being searched late yesterday. The nine men, who were being held at a police station in Coventry last night, are all family men, well known in their communities.

One was named locally as Amjad Mahmood, 29, a father of two young sons, who worked at his father's store. A man who identified himself as Mr Mahmood's brother, Ziah Khan, said he ran out of his own nearby home when he heard the police raid. "The little boys were shouting 'please don't take our father' over and over again," he said. "He is a very decent man, all he does is work. He is no terrorist. He doesn't have time for anything else - he never leaves the country."

It was unclear last night whether all those suspected of involvement in the alleged plot had been arrested, although David Shaw, assistant chief constable of West Midlands, said the motorway arrest "illustrates ... that this remains a dynamic, fluid operation". He added: "We are literally right at the foothills of what is a very, very major investigation."